Weak scattering theory applied to equatorial ionospheric scintillation for a wide range of parametric values

Abstract

The model of ionospheric fluctuations used by Booker and Ferguson (1978) to describe spread- F is applied to ionospheric scintillation in the band from 100 MHz to 10 GHz in equatorial regions. Calculations are based on long Isotropie field-aligned irregularities possessing an inverse power-law spectrum extending from an outer scale [wavelength/(2π)]linked to the properties of the neutral atmosphere down to an inner scale of the order of the ionic gyroradius. Spectral indices from 0 to 6 are considered, with special attention to the range from 1 to 4. The r.m.s. fluctuation of ionization density is assumed to be proportional to the ambient ionization density throughout the plasmasphere, but the effect is shown of removing the fluctuations at heights above 500, 750 and 1000 km. Using a height-distribution of phase-changing screens, calculations are made, for evening and presunrise conditions, of the mean square fluctuations both of phase and of fractional amplitude for situations in which an Earth terminal and a stationary satellite are both in the magnetic equatorial plane. Heights of equivalent single phase-changing screens are deduced for both phase and amplitude fluctuations; they are different from each other and from the height of maximum ionization density. It is concluded that the weak scattering theory can satisfactorily explain weak scintillation, but that amplitude scintillation at strengths of practical importance for radio communications requires the inclusion of refractive scattering in addition to diffractive scattering.